FOOD AND DRIXK. 235 



Rudolphi, averages IOI. The extremes recorded by them 

 were 96 and 106, the former in the narwhal, the latter in 

 a bat (Vespertilio Pipistrella). In birds, the average is as 

 high as 107 ; the highest temperature, 1 1 1*25, being in 

 the small species, the linnets, etc. Among reptiles, Dr. 

 John Davy found, that while the medium they were in was 

 75, their average temperature was 82 '5. As a general 

 rule, their temperature, though it falls with that of the 

 surrounding medium, is, in temperate media, two or 

 more degrees higher ; and though it rises also with that of 

 the medium, yet at very high degrees it ceases to do so, 

 and remains even lower than that of the medium. Fish 

 and Invertebrata present, as a general rule, the same tem- 

 perature as the medium in which they live, whether that 

 be high or low ; only among fish, the tunny tribe, with 

 strong hearts and red meat-like muscles, and more blood 

 than the average of fish have, are generally 7 warmer 

 than the water around them. 



The difference, therefore, between what are commonly 

 called the warm- and the cold-blooded animals, is not one 

 of absolutely higher or lower temperature ; for the animals 

 which to us, in a temperate climate, feel cold (being like 

 the air or water, colder than the surface of our bodies), 

 would, in an external temperature of 1 00, have nearly the 

 same temperature and feel hot to us. The real difference 

 is, as Mr. Hunter expressed it, that what we call warm- 

 blooded animals (birds and Mammalia), have a certain 

 " permanent heat in all atmospheres/* while the tempera- 

 ture of the others, which we call cold-blooded, is " variable 

 with every atmosphere." 



The power of maintaining a uniform temperature, which 

 Mammalia and birds possess, is combined with the want of 

 power to endure such changes of temperature of their bodies 

 as are harmless to the other classes ; and when their power 

 of resisting change of temperature ceases, they suffer serious 

 disturbances or die. 



